1. Field of the Invention
This invention relates to a low noise level automotive internal combustion engine, and more particularly to an engine equipped with a bearing beam structure for supporting a crankshaft in a manner to improve the mechanical strength of a cylinder block.
2. Description of the Prior Art
In connection with engine noise, noise emitted from a cylinder block skirt section and an oil pan is mainly caused by the vibration of the cylinder block itself. In order to reduce such vibration noise, it would appear sufficient to suppress the vibration, due to explosion torque, applied to a crankshaft by increasing the rigidity of the cylinder block. However, this unavoidably leads to an increase in cylinder block wall thickness and accordingly to a great increase in engine weight, thereby giving rise to new problems such as reduced fuel economy. In view of this, a variety of propositions have been made to improve the rigidity of the cylinder block while suppressing the increase in cylinder block weight. Of these propositions, attention has been paid to the employment of a bearing beam structure which securely connects a plurality of bearing caps for supporting the crankshaft, in order to improve the mechanical strength of bearing caps and engine parts associated with them.